Devices for describing arcs are commonly known. Such devices often are referred to as compasses and include two legs pivotably attached at one end. The free ends of the legs can thus be pivoted towards or away from one another. By attaching a marking instrument, such as a pencil, to one leg and holding the other leg at a fixed pivot point, the marking instrument can be rotated about the pivot point to form an arc of generally constant radius.
One problem with this type of device is the difficulty of maintaining one leg at a fixed pivot point while the other leg and attached marking instrument are rotated about that point. Some compasses include a sharp, needle-like point at the free end of one leg. However, as one might imagine, these compasses can be extremely dangerous, particularly in the hands of younger children. Other compasses have a suction cup or pad to hold the pivot leg in place. Problems also arise in maintaining the compass at the fixed pivot point and in locating the precise center point of the desired arc or circle. Some devices have a pointer within a suction cup to help a user locate the desired center point of the arc with greater precision. The suction cup, however, must either be made of transparent material or have some type of window so the pointer can be seen. These configurations tend to be complicated and difficult to use, particularly if the devices are to be used by children learning about shapes and basic geometry.
Another problem with existing compasses is maintenance of the constant radius while the arc or circle is formed. Many compasses simply use a pivot joint between the legs which has a certain level of friction to limit unintentional movement of the legs with respect to each other. However, if the user provides excess pressure on the compass while describing an arc or circle, the legs will tend to spread, resulting in an unsatisfactory arc. Again, this is particularly a problem with younger children who may be learning to use a compass and inadvertently apply more pressure than the frictional pivot joint can withstand.
Other compasses include a threaded bar extending through threaded bores in each of the legs to maintain the legs at a fixed distance with respect to each other. The threaded bar typically includes threads of opposite direction, i.e. threads turned in one direction at one leg and threads turned in the opposite direction at the other leg. This is necessary so both legs can either be expanded or drawn together by turning the single threaded rod. Such a system is more expensive to manufacture and is not particularly susceptible to the use of plastic components.
Existing compasses are also often awkward to hold and somewhat difficult to use because of their design. There are no large, comfortable surface areas for grasping by a user. Again, this is particularly disadvantageous for young children learning to use compasses since their hands may lack the dexterity required to manipulate conventional devices.
The present invention addresses the drawbacks of current compass devices.